The proteasome has been validated as a therapeutic target, as demonstrated by the recent FDA approval of bortezomib, a boronic acid proteasome inhibitor, for the treatment of multiple myeloma. However, other more highly proteasome-specific inhibitors that could have fewer toxic side effects have recently been described. These compounds include peptide epoxy ketones such as epoxomicin and peptide (b), described in U.S. Pat. No. 6,831,099, the contents of which are hereby incorporated by reference, and peptide (a), described in U.S. Provisional Application No. 60/569,096, filed May 7, 2004, the contents of which are hereby incorporated by reference. However, the low aqueous solubility of some of these compounds makes it difficult to formulate compositions with optimal bioavailability. Thus, additional methods of formulating peptide epoxy ketones are needed.